1. Field of the Invention
The present invention relates to an anti-wear, high-strength, damage-resistant rail used for sharp curves of a high-axle load railroad, more particularly, to a high-strength, damage-resistant rail in which the resistance to damage to a head top portion thereof is improved.
2. Background Information
A head of a rail has a head top portion, corner portions, head side portions and jaws. A conventional anti-wear, high-strength rail used in a track of sharp curves of a high-axle load railroad which uses wooden crossties is heat-treated such that the hardness of the corner and head side portions is equal to that of the head top portion. Therefore, the anti-wear properties of the rail corner portions are the same as those of the rail head portion.
However, contact between the wheels and the rails is complicated, and the contact pressure varies depending on the position of the rail head-wheel contact. In a sharp curve of a high-axle load railroad, large slip forces act on a rail gauge corner portion (i.e., an inner corner portion) and the rail head side surfaces. However, a large contact pressure acts on the rail head top portion and the rail gauge corner portion. As a result, the rail gauge corner portion and the rail head side portions of the conventional anti-wear, high-strength rail are worn much more than the rail head top portion. Therefore, the rail head top portion is always worn much less than the rail gauge corner portion, and a maximum contact pressure from each wheel acts on the central less-worn portion of the rail head top portion.
Since the contact state between the wheels and the conventional anti-wear, high-strength rail having uniform wear properties of the rail head is as described above, it takes a long period of time to fit rails to the wheels during an initial period of use of the rails. A local excessive contact stress lasts for a long period of time, and defects caused by fatigue tend to be formed. Even after the rails are brought into satisfactory fitness to the wheels, a maximum contact pressure acts on the rail head top portion of each rail. Decisive problems are not posed in this condition when wooden crossties are used to form a track. However, when concrete crossties are used to form a highly rigid track, an impactive maximum contact pressure generated upon passing of a rolling stock is increased. Therefore, damage called the surface contact fatigue typically occurs in the central rail head top portion.
In order to prevent the head check according to a conventional technique, a method of grinding and correcting a rail head surface layer prior to accumulation of fatigue in the rails is employed. However, this operation is time-consuming and costly. In addition, it is also difficult to determine an optimal grinding/correcting time.
In the meantime, U.S. Pat. No. 5,209,792 discloses a rail capable of preventing a head check generated in the center portion of the head top portion. This rail is formed such that the hardness of each of the corner portion and the head side portion is high, and the hardness of the head top portion is made 0.9 or less of that of either the corner portion or the head side portion. Thus, the hardness of the head top portion is decreased so as to raise the wearing rate of that portion, and the contact force at the head top portion is dispersed to lower the maximum contact stress, thus reducing the damage to the head top portion.
However, the generation of the damage to the head top portion depends on the contact stress, and the contact stress and its distribution depend on the distribution of the wearing speed of the head top portion, that is, the distribution of the head top portion in the rail width direction. Therefore, even if the range of the hardness of each of the corner portion and the head side portion, and the range of the hardness of the head top portion are defined as in U.S. Pat. No. 5,209,792, the damage reducing effect cannot always be obtained, or the life of rail may not be prolonged.
The present invention has been proposed so as to solve the above-described drawbacks of the high-axle load railroad, and the object thereof is to provide a long-life high-strength, damage-resistant rail, the rail head top portion of which has an appropriate hardness distribution, in which a fatigue accumulation is not locally concentrated on the rail head top portion, the contact fatigue damage resistance is excellent, thereby capable of reducing the maintenance cost of track.
According to a first aspect of the present invention, there is provided a high-strength, high damage-resistant rail consisting essentially of 0.6 to 0.85 wt % of C, 0.1 to 1.0 wt % of Si, 0.5 to 1.5 wt % of Mn, 0.035 wt % or less of P, 0.040 wt % or less of S, and 0.05 wt % or less of Al, the balance being Fe and inevitable impurities, and comprising corner and head side portions having a Brinell hardness (HB) of 341 to 405, and a head top portion in which a Brinell hardness of a site 20-mm distant from a central portion of the head top portion in a width direction is 341 to 405, and a hardness of the central portion of the head top portion is at least 10 lower in Brinell hardness (and preferably at least 10 to 50 lower in Brinell hardness), than that of the-site 20-mm distant from the central portion, a ratio of                                                         the              ⁢                              xe2x80x83                            ⁢              difference              ⁢                              xe2x80x83                            ⁢              between              ⁢                              xe2x80x83                            ⁢                              (                                                                                                                                                                                        the                              ⁢                                                              xe2x80x83                                                            ⁢                              Brinell                              ⁢                                                              xe2x80x83                                                            ⁢                              hardness                              ⁢                                                              xe2x80x83                                                            ⁢                              of                                                                                                                                                                                          the                              ⁢                                                              xe2x80x83                                                            ⁢                              central                              ⁢                                                              xe2x80x83                                                            ⁢                              portion                              ⁢                                                              xe2x80x83                                                            ⁢                              of                                                                                                                                                                                                                              the                        ⁢                                                  xe2x80x83                                                ⁢                        head                        ⁢                                                  xe2x80x83                                                ⁢                        top                        ⁢                                                  xe2x80x83                                                ⁢                        portion                                                                                            )                            ⁢                              xe2x80x83                            ⁢              and                        ⁢                          xe2x80x83                                                                                      (                                                                                                                                                                        the                            ⁢                                                          xe2x80x83                                                        ⁢                            Brinell                            ⁢                                                          xe2x80x83                                                        ⁢                            hardness                            ⁢                                                          xe2x80x83                                                        ⁢                            of                                                                                                                                                                            the   site   20-mm   distant                                                                                                                                                                                                          from                      ⁢                                              xe2x80x83                                            ⁢                      the                      ⁢                                              xe2x80x83                                            ⁢                      central                      ⁢                                              xe2x80x83                                            ⁢                      portion                                                                                  )                        ⁢                          xe2x80x83                                            ⁢          xe2x80x83            (                                                      the              ⁢                              xe2x80x83                            ⁢              Brinell              ⁢                              xe2x80x83                            ⁢              hardness              ⁢                              xe2x80x83                            ⁢              of              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              site                        ⁢                          xe2x80x83                                                                        20-mm   distant   from  the   central   portion                                )  
being 0.1 or less (preferably 0.09 or less), a hardness of a section between the central portion of the head top portion and the site 20-mm distant from the center in the width direction increases gradually from the central portion towards an outer side of the width direction, and a difference between an actual hardness of the section, and a hardness obtained by interpolating the hardness of the central portion of the head top portion and the hardness of the site 20-mm away from the center in the width direction by a straight line, is 10 or less in Brinell hardness.
According to a second aspect of the invention, there is provided a high-strength, high damage-resistant rail consisting essentially of 0.6 to 0.85 wt % of C, 0.1 to 1.0 wt % of Si, 0.5 to 1.5 wt % of Mn, 0.035 wt % or less of P, 0.04 wt % or less of S, and 0.05 wt % or less of Al, containing at least one of 0.05 to 1.5 wt % of Cr, 0.01 to 0.20 wt % of Mo, 0.01 to 0.10 wt % of V, 0.1 to 1.0 wt % of Ni and 0.005 to 0.15 wt % of Nb, the balance being Fe and inevitable impurities, and comprising corner and head side portions having a Brinell hardness (HB) of 341 to 405, and a head top portion in which a Brinell hardness of a site 20-mm distant from a central portion of the head top portion in a width direction is 341 to 405, and a hardness of the central portion of the head top portion is at least 10 lower in Brinell hardness (and preferably at least 10 to 50 lower in Brinell hardness), than that of the site 20-mm distant from the central portion, a ratio of                                                         the              ⁢                              xe2x80x83                            ⁢              difference              ⁢                              xe2x80x83                            ⁢              between              ⁢                              xe2x80x83                            ⁢                              (                                                                                                                                                                                        the                              ⁢                                                              xe2x80x83                                                            ⁢                              Brinell                              ⁢                                                              xe2x80x83                                                            ⁢                              hardness                              ⁢                                                              xe2x80x83                                                            ⁢                              of                                                                                                                                                                                          the                              ⁢                                                              xe2x80x83                                                            ⁢                              central                              ⁢                                                              xe2x80x83                                                            ⁢                              portion                              ⁢                                                              xe2x80x83                                                            ⁢                              of                                                                                                                                                                                                                              the                        ⁢                                                  xe2x80x83                                                ⁢                        head                        ⁢                                                  xe2x80x83                                                ⁢                        top                        ⁢                                                  xe2x80x83                                                ⁢                        portion                                                                                            )                            ⁢                              xe2x80x83                            ⁢              and                        ⁢                          xe2x80x83                                                                                      (                                                                                                                                                                        the                            ⁢                                                          xe2x80x83                                                        ⁢                            Brinell                            ⁢                                                          xe2x80x83                                                        ⁢                            hardness                            ⁢                                                          xe2x80x83                                                        ⁢                            of                                                                                                                                                                            the   site   20-mm   distant                                                                                                                                                                                                          from                      ⁢                                              xe2x80x83                                            ⁢                      the                      ⁢                                              xe2x80x83                                            ⁢                      central                      ⁢                                              xe2x80x83                                            ⁢                      portion                                                                                  )                        ⁢                          xe2x80x83                                            ⁢          xe2x80x83            (                                                      the              ⁢                              xe2x80x83                            ⁢              Brinell              ⁢                              xe2x80x83                            ⁢              hardness              ⁢                              xe2x80x83                            ⁢              of              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              site                        ⁢                          xe2x80x83                                                                        20-mm   distant   from  the   central   portion                                )  
being 0.1 or less (preferably 0.09 or less), a hardness of a section between the central portion of the head top portion and the site 20-mm away from the center in the width direction increases gradually from the central portion towards an outer side of the width direction, and a difference between an actual hardness of the section, and a hardness obtained by interpolating the hardness of the central portion of the head top portion and the hardness of the site 20-mm distant from the center in the width direction by a straight line, is 10 or less in Brinell hardness.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.